Selectively cooled motive fluid trap for a vacuum steam pump



March 18, 1969 3,433,297

M. KOHLER SELECTIVELY COOLED MOTIVE FL TRAP FOR A VACUUM S M PUM FiledAug. 1967 Jnvenfor:

5 A77'0ENEVS United States Patent C 3,433,297 SELECTIVELY COOLED MOTIVEFLUID TRAP FOR A VACUUM STEAM PUMP Marcel Kohler, Balzers,Liechtenstein, assignor to Balzers Patentnnd Lizenz-Anstalt, Balzers,Liechtenstein Filed Aug. 21, 1967, Ser. No. 661,903 Claims priority,application Switzerland, Aug. 23, 1966,

12,25 1/ 66 US. Cl. 165-40 6 Claims Int. Cl. F28b 9/10; F28d 1/06ABSTRACT OF THE DISCLOSURE A motive fluid trap for a vacuum steam pumpformed by a trap housing mounted on the steam pump. Means are disposedwithin the trap housing for condensing the motive or fluid vaporincluding a support block secured to the trap housing. A nozzle cap fora nozzle, located in the upper part of the pump, is positioned justbelow the support block. A shield for the nozzle cap is dependentlysecured to a thermally responsive support element mounted on the blockwhereby the shield is movably positionable with respect to the nozzlecap in relation to the temperature to which the thermally responsivesupport element is exposed within the trap housing.

The prior art The present invention is directed to a motive fluid trapfor vacuum steam pumps and, more particularly, to a motive fluid trapwhich employs different coolants adapted to operate at differenttemperatures.

The ability to cool a motive fluid trap in a vacuum steam pump todifferent temperatures would be particularly useful in adapting the pumpto various operating conditions. In selectively cooling the motive fluidtrap it is useful if different coolants capable of operating atdifferent temperatures are employed. When a stronger motive fluid returnflow is permissible, or if the pump is separated from its receiverduring operation, as by a plate valve, then using water as the coolantis appropriate. However, if the motive fluid vapor pressure in thereceiver is to be kept as low as possible to obtain an optimum highvacuum then cooling with liquid nitrogen is preferable. If a coolant isemployed which would tend to solidify or freeze the motive fluid withinthe trap, it is important to limit the amount of freezing as much aspossible, because the operation of the pump would be disturbed by anyconsiderable loss of motive fluid due to freezing.

It has been known in the past to use a steam jet diffusion pumpemploying a condenser disposed between the pump and the space to beevacuated, see German Pat. No. 1,000,965. In this arrangement thecondenser is maintained at a temperature of 40 or less, however, itutilizes a condenser plate located in the path of the gas particles andthe temperature of the plate is maintained high enough that the motivefluid from the pump in the vicinity of the plate condenses thereon onlyin liquid form.

For another trap employed to cool steam to a low temperature bycondensing vapors in a vacuum system, see German provisional Pat. No.1,071,890. In this arrangement the vapor discharged into the coolantvessel or trap evaporates toward the exterior or surface of the trap andin so doing, it cools the separating surfaces within the connecting linebetween the vacuum receiver and the motive fluid pump. Accordingly, theseparation surfaces are at a temperature whereby the condensable vaporsare separated out in the liquid state, and a passage of the condensedfluid is provided from the coolant vessel whereby the condensed fluidserves to cool other separation surfaces whose temperature is above thatof the coolant fluid.

3,433,297 Patented Mar. 18, 1969 These known arrangements were notintended for selective operation with coolants of differenttemperatures, and as a result no problem arose due to the effect ofdifferent temperatures operating on the structure of the coolant trapand its associated pump.

Summary of the invention It has been found that a considerable portionof the motive fluid return flow in a vacuum steam pump originates in thezone of the motive steam jet from the uppermost nozzle, and this returnflow can be greatly reduced by providing the zone with an annular orhood-shaped shield for the cap on the nozzle. Further, the shield canalso serve to protect other parts of the steam coolant trap againstexcessive heating by the radiation from the hot nozzle. Where a shieldis employed over the nozzle cap, and different fluids are used toselectively cool the trap, such as water and liquid nitrogen, due to thedifferent temperatures of the fluids employed, a problem results in thatif good heat transmission exists between the trap and the shield whenthe lower temperature coolant is employed, there is a tendency for thesteam to freeze on the surface of the trap and thereby disturb theoperation of the pump. Conversely, if a heat resistance is placedbetween the shield and the coolant trap, which prevents propercondensation of the motive fluid, then where water is used an ineffective cooling effect is obtained on the shield and the advantages soughtto be obtained by the use of this structure are largely offset. It wouldbe possible to provide a separate cooling arrangement for the shieldusing a special coolant to attain the proper operating temperature forthe shield, however, such an arrangement would be costly and complicatedto operate.

The present invention is directed to a motive fluid trap for a vacuumsteam pump wherein the steam is condensed by selectively cooling it withcoolants of different operating temperatures. In accomplishing thisresult, a shield is provided over the nozzle of the pump, and the shieldis arranged so that it can be movably positioned in relationship to thenozzle cap for assuring the proper operating conditions for the vacuumsteam pump.

Accordingly, it is a primary object of the present invention to utilizea thermally responsive support member in a motive fluid trap for avacuum steam pump which will respond to the temperature within the trapto properly position and support a shield member in relationship to anozzle cap in the vacuum steam pump itself.

Another object of the invention is to utilize a bimetallic element asthe thermally responsive support element for the shield in a motivefluid trap selectively cooled by coolants of different temperatures.

Yet another object of the present invention is to provide a combinedmotive fluid trap and vacuum steam pump which permits selective coolingof the motive fluid within the trap while maintaining the optimumefficiency of the pump regardless of the coolant temperature employed.

Therefore, the present invention is directed to a motive fluid trapwherein different coolants operating at different temperatures can becirculated to condense the vaporized motive fluid employed in a vacuumsteam pump. The trap is positioned above the uppermost nozzle of thevacuum steam pump and a cap separates the nozzle and the trap. The trapis comprised of a support assembly which includes a thermally responsivesupport element and a shield dependably supported from the supportelement and movably positionable in relationship to the nozzle cap. Inresponse to the temperature within the trap the support element eitherexpands or contracts and accordingly positions the shield which issecured to it.

The support assembly for the shield, and more specifically its thermallyresponsive support element, must be adapt ed to the different coolantswhich are used in the trap whereby the shield supported from the elementwill assume a position relative to the trap such that the temperature ofthe shield is within permissible limits for reliable operation of thepump. In other words, if a coolant such as water at 15 C. is employed,the heat transmission from the trap to the shield, which is determinedby the amount of radiation and heat conduction from the nozzle, must bebetter than exists where a lower temperature coolant, such as liquidnitrogen, is utilized. One successful embodiment of the inventionconsists in a construction wherein a thermally responsive supportelement arranged within the trap permits the shield to touch the nozzlecap when a higher temperature coolant is employed but which causes theshield to be spaced from the nozzle cap when the arrangement is beingcooled by a lower temperature coolant, such as a liquid gas.

The various features of novelty which characterize the invention arepointed out with particularity in the claims annexed to and forming apart of this specification. For a better understanding of the invention,its operating advantages and specific objects attained by its use,reference should be had to the accompanying drawing and descriptivematter in which there is illustrated and described a preferredembodiment of the invention.

Description of the drawing The drawing discloses a vertical sectionalview of a coolant trap and a portion of a vacuum steam pump embodyingthe present invention.

Detailed description of the invention In the drawing the upper portionof a vacuum steam pump is shown formed by a housing 1 with a flange 2disposed at its upper end. Secured to the flange 2 is another flange 3forming part of a motive fluid trap 4 which extends vertically upwardabove the housing 1 of the vacuum steam pump. Within the space 12 in thehousing 4 a plurality of right angle collection plates are disposed invertically spaced arrangement supported by a number of struts from asupport block 11 which is supported on the housing 4. The collectionplates 59 are cooled by circulating a coolant through tubes 13 securedto the plates. In this arrangement the coolant flowing through the tubes13 cools the collection plates, which, in turn, condense the steam vaporas it passes over them but permits the gas mixed with the vapor toescape from the space 12.

On the upper surface of the block 11, uprights 14 and 15 support ahorizontally arranged thermally responsive bimetallic element 16. Theblock also contains a centrally arranged bore or opening 17 throughwhich extends a support rod 18 attached at its lower end to a shield andat its upper end to the bimetallic element 16. The shield 20 ispositioned above the nozzle cap 19:: located on the nozzle 19 of thevacuum steam pump. The position of the shield relative to the nozzle capis determined by the position assumed by the thermally responsive sup-'port element 16 within the motive fluid trap.

It can be readily appreciated that, with decreasing temperatures, thethermally responsive support element 16 will contract and will assume aflat or horizontal position, and as the temperature within the trapincreases, the support element 16 will tend to expand and with theuprights 14 and 15 set relatively stationary, the support element 16will tend to curve downwardly with its center, to which the rod 18 issecured, assuming the lowermost position. Since the shield is secured tothe rod 18, the position of the shield will depend on the positionassumed by the support element. When the higher temperature coolant isused, the shield will be in its lower position supported directly on thenozzle cap 19a and as the temperature of the coolant decreases, theshield Will lift off the cap to a position spaced some distance from itdepending upon the operating conditions desired for the pump.

While one specific embodiment of a thermally responsive support elementhas been shown in the drawing, based on the principle described herein,it will be appreciated that a number of different support elements maybe employed which are sensitive to temperature variations within thetrap and which will provide the proper orientation of the shieldrelative to the nozzle cap of the pump, based on the temperature withinthe trap. The arrangement employed will depend on the operatingconditions of the pump and must be capable of providing reliable andefficient operation.

While a specific embodiment of the invention has been shown anddescribed in detail to illustrate the application of the inventiveprinciples, it will be understood that the invention may be embodiedotherwise without departing from such principles.

What is claimed is:

1. A motive fluid trap for a vacuum steam pump, whereing differentcoolants operating at different temperatures can be circulated tocondense the vaporized motive fluid, comprising a vacuum steam pumpnozzle, a cap positioned on said nozzle, a trap member dis-posed abovesaid nozzle comprising a support assembly including a thermallyresponsive support element, a shield located below said support assemblyand disposed above and movably positionable in relationship to saidnozzle cap, said shield dependently secured to said thermally responsivesupport element whereby as the support element expands and contracts inresponse to the temperature Within said trap member the shield supportedfrom the thermally responsive support element will move toward and awayfrom the nozzle cap respectively.

2. A motive fluid trap as set forth in claim 1 wherein said shield ismovably positionable between a lower position in contact with saidnozzle cap and an upper position spaced from said nozzle cap.

3. A motive fluid trap as set forth in claim 2 wherein said trap membercomprises a housing, said support assembly located within said housingand comprising a block member secured to said housing and having anopening arranged therethrough, said thermally responsive support elementmounted on said block member, a vertically oriented support rodextending through the opening in said block member and secured at itsupper end to said support element and at its lower end to said shield.

4. A motive fluid trap as set forth in claim 3 wherein a pair of supportcolumns extend upwardly from said block member, said thermallyresponsive support element is horizontally oriented and is attached toand extends between said columns.

5. A motive fluid trap as set forth in claim 4 wherein said thermallyresponsive support element comprises a bimetallic element.

6. A motive fluid trap as set forth in claim 3 wherein a plurality ofannular collection plates are positioned in said trap member and aresupported theerin by said block member, and conduit means located withinsaid trap member for circulating coolant fluid therethrough for coolingthe surfaces of said collection plates.

References Cited UNITED STATES PATENTS 1,323,813 12/1919 Baruch 731,461,726 7/1923 Crafts 165-73 3,175,373 3/1965 Holkeboer et al 165111LLOYD L. KING, Primary Examiner.

C. SUKALO, Assistant Examiner.

US. Cl. X.R.

